A three-detector observation of a binary black hole coalescence

This afternoon, the LIGO Scientific Collaboration and Virgo Collaboration announced the fourth significant detection of gravitational waves. This event, dubbed GW170814, originated from the inspiral and collision of two black holes, located more than a billion light years away. The two black holes had estimated masses of 31 and 25 solar masses, with roughly 3 solar masses’ worth of energy emitted leading up to the collision, similar to those binaries seen previously through gravitational waves.

This detection is the first by the Advanced Virgo interferometer, which joined the twin Advanced LIGO detectors on August 1, 2017, near the end of LIGO’s second observational campaign. The combination of three gravitational wave detectors allowed the teams to determine the position of GW170814 much more precisely than for previous gravitational wave signals. For this event, the addition of Virgo to the detector network improved the localisation capabilities by an order of magnitude. This major advance will assist astronomers seeking to follow up gravitational wave detections by searching for electromagnetic signals such as light, radio waves, and X-rays, as well as neutrinos and other cosmic rays, an effort known as “multi-messenger astronomy.”

Researchers at CITA who are members of the LIGO Scientific Collaboration played an important role in this milestone. In particular, CITA researchers helped lead the effort to analyse GW170814 and characterize the binary, providing the best estimates for the masses and spins of the black holes and the location of the merger in the sky. CITA researchers also assist in cross-checking gravitational wave signals like GW170814 against supercomputer simulations of black hole mergers, and in developing the rapid search techniques that first identified the gravitational wave signal. An example simulation of the merger of two black holes with masses consistent with GW170814 is seen below*. More information about CITA’s involvement in LIGO and gravitational waves can be found on our research page.